1. Field of the Invention
The present invention is directed to liquefied gas containers and more particularly to containers for storing and delivering liquefied gas in either gas or liquid form.
2. Description of Related Art
Heretofore, containers for low temperature liquefied gas have included an inner stainless steel shell that contains the low temperature liquefied gas and an outer stainless steel or carbon steel shell that encloses the inner shell and is sealed to it. The space between the shells is evacuated and the connections and support structures between the inner and outer shell are held to a minimum, because each such connection and structure is a conduit for heat transfer. It has been the practice to provide a passage or channel at the top of the container from the outside to inside the inner shell through a thin wall stainless steel tube, sometimes called a necktube, that is sealed to an opening in the inner shell and projects through and is sealed to an opening in the outer shell. The thin wall tube provides access to the inner shell from outside of the container and is thin walled so that it will be a minimum conductor of heat from the outer shell to the inner shell.
One of the problems with such prior containers is that the top end of the inner shell is supported within the outer shell only by the necktube. This suspension, with no support at the bottom of the container, acts like a pendulum when the container falls on its side or is otherwise laterally impacted, and the necktube will often kink, buckle or crack. When the container is tilted, the necktube will often break or rupture. If the inner shell is also supported by the outer shell at the bottom of the container, the bottom support can be of very sturdy construction and made of low thermal conductivity material. Where such a lower or bottom support is used, the lateral forces on the necktube at the top when the container is tipped may be worse, because the inner shell cannot swing as a pendulum within the outer shell and the necktube tries to assume a reverse bend which results in maximum flexural stress and possible fracture.
A primary problem encountered in attempting to provide increased protection of the necktube is that such protection generally requires additional areas of contact between inner components and the outer shell, thus creating additional conduction paths between either the neck tube or the inner shell and the outer shell. Prior attempts to provide improved support of the inner shell or vessel for protection against necktube rupture can be seen in U.S. Pat. No. 4,674,289, to Andonian, and U.S. Pat. No. 4,538,445, to Remes.
The Andonian patent employs a fairly intricate suspension arrangement of the inner vessel in an attempt to provide improved protection against rupture of the necktube. The Andonian container employs a necktube which extends from the inner shell opening through the outer shell opening and attaches to an external flange. Surrounding the necktube and extending downwardly from the external flange is a second cylindrical support tube having a larger diameter than the necktube thereby leaving a space between the tubes. The outer support tube is sealed to the opening in the outer vessel, and extends inwardly therefrom in a telescoping manner with respect to the necktube. The support tube carries an inwardly extending annular bumper which contacts the necktube at a reinforced section of the necktube near the joint with the inner shell.
A disadvantage of this support is that the intricacy of the design makes fabrication of such vessels more difficult. Additionally, the necktube in the Andonian patent is not completely disposed within the outer shell, and extends upwardly through an opening in the upper head, where it is surrounded only by the support tube. Such a design may result in increased thermal losses to the atmosphere compared with designs wherein the necktube is disposed completely within the confines of the outer shell.
The Remes patent employs an annular abutment extending from a wall of the outer vessel across the space between the outer vessel and inner vessel, but short of contact with the inner vessel wall. While such a design avoids the complexity of the necktube connection shown in Andonian, it possesses the disadvantage that the annular abutment or ring contacts the wall of the outer vessel around the entire circumference thereof. Thus, although direct contact between the inner container and the annular abutment will not generally occur, movement of the inner container relative to the outer shell will cause the insulation between the inner container and the annular abutment to be compacted and damaged resulting in increased thermal losses. Such compaction of the insulation may occur either as a result of minor or major impacts to the container causing the inner vessel to shift with respect to the outer vessel, or the contact could be the result of out-of-tolerance manufacturing.
Another feature of prior containers is that the vaporizer circuit is generally a copper tube encircling the inner shell several times like a coil to provide a large surface area for conducting heat from the outer shell into the liquid to vaporize it as it is drawn through the copper tube. At the top of the container the copper tube connects to a stainless steel tube that penetrates and is welded to the outer shell and then to a gas output valve outside the container. This configuration of the vaporization coil has the drawback that the coils occupy space between the inner and outer vessels, making for a tighter fit, which may preclude the use of more compact container designs.
The copper vaporizer coil, in the container described above, is soldered to the inside of the stainless steel or carbon steel outer shell. In order to solder these metals, corrosive flux must be used which leaves a residue which must be cleaned, adding to the manufacturing cost of the container. Further, if the joint is not correctly cleaned, the remaining residue may later produce gases in the vacuum, reducing the effectiveness of the vacuum space.
Furthermore, maximum thermal utilization of available surface area is normally compromised to avoid using excessive lengths of copper tubing.
It is therefore a principal object of the present invention to provide a liquefied gas container having an improved lateral support structure extending between the outer and inner vessels for preventing damage to the necktube.
A further object of the present invention to provide a liquefied gas container with such an improved support structure which has the further advantage of reducing or substantially eliminating the thermal conduction paths associated with the support structure.
Another object of the present invention to provide a lateral support structure for enhancing protection of the necktube which employs a floating support disc having a double heat break between a collar surrounding the necktube and the interior wall or upper head of the outer shell.
Still another object of the present invention to provide a liquefied gas container having an inner vessel surrounded by an outer shell capable of delivering the gas in both liquid and gaseous forms, the container having a vaporizer circuit for vaporizing the liquefied gas, the vaporizer circuit being integral with the wall which forms the outer shell.
It is a further object of the present invention to provide a liquefied gas container having an improved bottom mounted gas withdrawal line feeding the vaporizer circuit.
It is a further object of the present invention to provide a liquefied gas container having improved gas and liquid withdrawal circuits wherein a gas withdrawal line is disposed telescopically within a liquid withdrawal line.
It is still a further object of the present invention to provide a liquefied gas container having an improved economizer circuit utilizing a constant bleed orifice, the circuit being in communication with an upper container gas space and the gas line circuit.
Another object of the present invention is to provide an improved liquefied gas container having two walls sealed together and evacuated between the walls for low heat transfer constructed such that a liquid is drawn from the container either through a heat exchanger by which it is converted to a gas and fed on demand as a gas or directly without heat exchange as a liquid to a user. The advantage of such containers over conventional high pressure gas containers for the same gas is that the gas is stored as a low (cryogenic) temperature liquid at a relatively low pressure and the volume of the liquid stored is substantially less than would be the volume of the high pressure gas in conventional high pressure containers.